Re: [Qemu-devel] [PATCH v5 02/35] target/arm: Implement SVE Contiguous Load, first-fault and no-fault

[Richard Henderson <richard.henderson@linaro.org>]

On 06/22/2018 09:04 AM, Peter Maydell wrote:
> On 21 June 2018 at 02:53, Richard Henderson
> <richard.henderson@linaro.org> wrote:
>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> ---
>>  target/arm/helper-sve.h    |  40 ++++++++++
>>  target/arm/sve_helper.c    | 156 +++++++++++++++++++++++++++++++++++++
>>  target/arm/translate-sve.c |  69 ++++++++++++++++
>>  target/arm/sve.decode      |   6 ++
>>  4 files changed, 271 insertions(+)
>>
>> diff --git a/target/arm/helper-sve.h b/target/arm/helper-sve.h
>> index fcc9ba5f50..7338abbbcf 100644
>> --- a/target/arm/helper-sve.h
>> +++ b/target/arm/helper-sve.h
>> @@ -754,3 +754,43 @@ DEF_HELPER_FLAGS_4(sve_ld1hds_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>>
>>  DEF_HELPER_FLAGS_4(sve_ld1sdu_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>>  DEF_HELPER_FLAGS_4(sve_ld1sds_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +
>> +DEF_HELPER_FLAGS_4(sve_ldff1bb_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldff1bhu_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldff1bsu_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldff1bdu_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldff1bhs_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldff1bss_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldff1bds_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +
>> +DEF_HELPER_FLAGS_4(sve_ldff1hh_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldff1hsu_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldff1hdu_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldff1hss_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldff1hds_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +
>> +DEF_HELPER_FLAGS_4(sve_ldff1ss_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldff1sdu_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldff1sds_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +
>> +DEF_HELPER_FLAGS_4(sve_ldff1dd_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +
>> +DEF_HELPER_FLAGS_4(sve_ldnf1bb_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldnf1bhu_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldnf1bsu_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldnf1bdu_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldnf1bhs_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldnf1bss_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldnf1bds_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +
>> +DEF_HELPER_FLAGS_4(sve_ldnf1hh_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldnf1hsu_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldnf1hdu_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldnf1hss_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldnf1hds_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +
>> +DEF_HELPER_FLAGS_4(sve_ldnf1ss_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldnf1sdu_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +DEF_HELPER_FLAGS_4(sve_ldnf1sds_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> +
>> +DEF_HELPER_FLAGS_4(sve_ldnf1dd_r, TCG_CALL_NO_WG, void, env, ptr, tl, i32)
>> diff --git a/target/arm/sve_helper.c b/target/arm/sve_helper.c
>> index 4e6ad282f9..6e1b539ce3 100644
>> --- a/target/arm/sve_helper.c
>> +++ b/target/arm/sve_helper.c
>> @@ -2963,3 +2963,159 @@ DO_LD4(sve_ld4dd_r, cpu_ldq_data_ra, uint64_t, uint64_t, )
>>  #undef DO_LD2
>>  #undef DO_LD3
>>  #undef DO_LD4
>> +
>> +/*
>> + * Load contiguous data, first-fault and no-fault.
>> + */
>> +
>> +#ifdef CONFIG_USER_ONLY
>> +
>> +/* Fault on byte I.  All bits in FFR from I are cleared.  The vector
>> + * result from I is CONSTRAINED UNPREDICTABLE; we choose the MERGE
>> + * option, which leaves subsequent data unchanged.
>> + */
>> +static void __attribute__((cold))
> 
> attribute cold was first introduced in GCC 4.3. As of
> commit fa54abb8c29 I think we still support gcc 4.1,
> so we need to hide this behind a QEMU_COLD or something I think, eg
> 
> #ifndef __has_attribute
> #define __has_attribute(x) 0 /* compatibility with older gcc */
> #endif
> 
> #if __has_attribute(cold) || QEMU_GNUC_PREREQ(4, 3)
> #define QEMU_COLD __attribute__((cold))
> #else
> #define QEMU_COLD
> #endif
> 
> (gcc added __has_attribute in gcc 5, which is nice.)

Ah, good archaeology.

But I think I'll just drop this.  I put it in there as a hint that it won't be
called, but the x86_64 code generation for putting this into the .text.unlikely
section is really ugly.

> 
>> +record_fault(CPUARMState *env, intptr_t i, intptr_t oprsz)
>> +{
>> +    uint64_t *ffr = env->vfp.pregs[FFR_PRED_NUM].p;
>> +    if (i & 63) {
>> +        ffr[i / 64] &= MAKE_64BIT_MASK(0, (i & 63) - 1);
> 
> Should this really have a - 1 here? (i & 63) will
> be anything between 1 and 63, so I would have expected
> the set of masks to be anything from "1 bit set" to
> "63 bits set", not "0 bits set" to "62 bits set".

We want to zero bits I to OPRSZ-1, which means retaining bits 0 to I-1.
But you're right that for e.g. I==65 this will produce ~0ULL >> 64.
I'll re-work this.


r~